More parts on the dipper handle booms - the back end plugs. These are half-round pieces that fit into the ends, sealing up the core and most likely is rounded to make it easier to fit the dipper through the center gap in the main boom when setting up at a new site (they would remove the main and dipper booms and transport them on a separate flatcar when moving to a new site by rail). Since there would be nothing to hold onto if I cut the parts to length first, I rounded the ends on the rotary table with the whole bar intact - did one at each end of the bar.The end mill would not reach all the way down in one cut, so it was done in two sets of passes. On the second pass, I stopped just short of the table and left a thin sliver that I filed off later.Then, switched out the rotab for the vise, and started cutting the tenon that will slip into the end of the boom. First cut the top, then the sides, lining up the sides to meet the edge of the top cut.And finished with the bottom cut, meeting up with the sides.The parts were cut off the bar, and test fit:The overhang at the bottom will overlap the end of the gear rack. Test fit was good, so drilled, riveted, and sanded the rivets off flush just like before.Also, as I mentioned the other day, I tapered the top of the yoke on the bucket, which I had forgotten to do when I made the yoke. Set it up in the vise on the tilt table, and took a few cuts with it tilted a couple of degrees, then sanded the corners to ease the edges. Looks much better, was too chunky before, did not match the original shape.So, next is to make the small lever that the door release chain attaches to, then on to a fun part, making the pinion gears and the gear racks for the bottom of the dipper booms!

Update on the discussion about the wood core in the booms: I found this picture in their catalog nbr 50, showing that the oak is in three pieces stacked up for the inside of the boom. It does not say which model shovel this was for, or whether this was the main or dipper boom.You can see that the grain is mostly on edge, not flat, though the top piece is at a 45 degree angle - they are not taking the same care that needs to be done for selecting pieces for bending and laminating for fine furniture, obviously, but it is plenty sturdy.I looked back through my photos of the booms on the shovel here, and can see some evidence in the grain that they did stack very thick boards for the large deadwood spacers between the main booms as well, with the seams also running horizontally and bolts through vertically. The end spacer piece on the dipper appears to be one slab, probably since that one is much narrower overall - the spacers on the main boom are huge, and would have included heartwood if cut from one piece.Details inside details!

Well, that was an interesting trip through the gear design/cutting books (Ivan Law and Jones/Ryffel books) to learn how to design a gear rack to fit an involute gear. Definitely going to need some chocolate chip therapy to get the brain to cool down!

Neither book gives a complete diagram and set of formulas for laying out the gear rack, but between the two its all there. Here is what I wound up with, assuming the module 0.6 gear driving the rack, drawn up in Fusion360 and dimensioned out as a 2D drawing:It looks correct to me, at least at the moment. Hopefully its right, will look again later with fresh eyes and see if I spot any glaring brain-farts. If any of you spot anything, please let me know!Assuming this looks plausible, I am going to start by cutting the gear, do some more spot checks on that, then grind up a single-point fly cutter to cut the rack with. If it was a lot larger I would be able to make it with a slitting saw and appropriate setups on the mill, but its pretty small spacing - the gear is only a little over 7" in diameter on the real thing, and this is 1/16th that size, so the tooth size gets pretty small. Hopefully it works out big enough to be functional.

If you have never seen it 'The Engineer' is still going, it's full of useful information and many what would now be called 'newsbytes' Founded in 1856, see Wikipedia. Published in the UK but covers the whole World, sometimes you might not think anything interesting occurs in the UK anymore such is the worldwide coverage. Graces guide has links for mags up to about 1960. It's never been chea\p to subscribe to but is chases the development of all sorts of machines from the initial conception right through to implemtation.

On Graces Guide there are links by company - all the shovel manufacturers we know of have mentions. Marion, Bucyrus and Rustons all feature, sometimes with picures of the intenals of their workshops.

Today it is essential reading if you are building jet engines, nuclear power plant and anything approaching the cutting edge.

If you have never seen it 'The Engineer' is still going, it's full of useful information and many what would now be called 'newsbytes' Founded in 1856, see Wikipedia. Published in the UK but covers the whole World, sometimes you might not think anything interesting occurs in the UK anymore such is the worldwide coverage. Graces guide has links for mags up to about 1960. It's never been chea\p to subscribe to but is chases the development of all sorts of machines from the initial conception right through to implemtation.

On Graces Guide there are links by company - all the shovel manufacturers we know of have mentions. Marion, Bucyrus and Rustons all feature, sometimes with picures of the intenals of their workshops.

Today it is essential reading if you are building jet engines, nuclear power plant and anything approaching the cutting edge.

Jerry

Hi Jerry,

I've browsed it a couple of times, an amazing amount of info there, some companies/engines more than others, but well worth the look.

A few more parts today. Started out by making up the little lever that the release chain that the bucket door latch goes to, then a rope from there leads back to the secondary operator on the turntable. From the old photos I've seen, the rope section actually has 4 or 5 feet of chain at the lever end, probably keeps it from blowing around the lever on windy days.Also, got the two small gears made that will engage the rack on the bottom of the dipper boom. They are 17 tooth, and the closest standard size to the real one after scaling down is a Module-0.6 cutter. Fortunately, that cutter set was one of the things on my Christmas list, so it has just gotten its first run in the machine. With a length of bronze bar held in the 4-jaw (trust it not to slip more than the 3-jaw when cutting gears), and the end turned down to size and drilled/reamed for the .125" shaft it will get, I transferred the chuck over to the rotary table (set vertically) on the mill, centered the cutter, moved it in for the cut, and started the passes for each tooth. Here it is partway around:and all done:Then, moved the chuck back to the lathe, and parted off the two gears. Here they are along with the lever:A few measurements on the gears verify the diagram I made of the rack, so next I'll take a 1/4" lathe tool blank and see if I can grind the tip for the teeth on the rack...

I've only had a couple of goes at gear chopping but if you use the 'trapped feeler gauge' method I could move the cutter up & down by a fair bit and still the blade was vertical. A gear cutter edge being a fairly large radius the procedure does not work as it does 'between centres' ?

I've only had a couple of goes at gear chopping but if you use the 'trapped feeler gauge' method I could move the cutter up & down by a fair bit and still the blade was vertical. A gear cutter edge being a fairly large radius the procedure does not work as it does 'between centres' ?

Dave

Hi Dave,

Centering it by looking at the outer edge is tough since its such a shallow curve, so in this case I cranked the table over so the tip of the cutter was at the shaft hole on the end, and centered the height by eye - handy that I am quite nearsighted, so if I take off my glasses and moving in close its like using a magnifier. For the normal and farsighted a magnifying glass would work. I got it within a thou or three, which is plenty close enough. On large gears with large bores, I like to chuck up a rod turned to a point before chucking up the real part, gives a easy to see reference.